1. Field of the Invention
The present invention relates to the development of electrographic images and more particularly to electrographic apparatus having an improved configuration for developing such images with single component developer.
2. Description of Prior Art
The use of an applicator member is a well known technique for developing an electrographic image member with dry toner particles. In general this technique involves the attracting of successive quantities of developer to the applicator and transporting the attracted developer into a transfer relation with successive portions of the image member. Magnetic brushes are a common form for such applicator members and usually have a cylindrical periphery on which developer is transported. Magnetic brushes are useful with single-component developer, wherein the toner is itself magnetic, and with multicomponent developers, wherein a magnetic carrier such as iron particles is utilized in mixture with the toner.
In most, if not all, development systems using applicator members, it is highly desirable to maintain certain nominal development conditions at the transfer interface, i.e., the zone between the developer and the image member. An important one of these nominal conditions is the spacial relation of the image member and the toner on the applicator; however, due to the dynamic nature of applicator development systems, a nominal spacial relation is quite difficult to maintain. If nominal spacing is not positively maintained, a temporary decrease in developer on the applicator can cause incomplete development. However, when nominal spacing is positively maintained, a temporary increase in developer on the applicator can cause image smearing and/or photoconductor abrasion.
U.S. Pat. No. 4,013,041 has disclosed an approach for alleviating these problems in plain paper copiers which have reusable image members. Specifically, the photoconductor is passed over the development zone in a slackened condition and under control of guide means so as to "float" with dynamic changes at the photoconductor-applicator interface. However, even more positive control of the spacing would be desirable. In copiers wherein the copy sheet is itself developed, another effective technique is available for maintaining the image member in contact with the developer. Specifically, the beam strength of the paper copy sheet is used to bias its image surface against the toner applicator. This approach is not readily available, however, in plain paper copiers of the type wherein the reusable image member must move repeatedly around a fixed copying path for development and transfer of successive toner images.